1. Field of the Invention
The present invention relates to a yoke of a speaker and a method for making the same, and more particularly, to a yoke of a speaker that has relatively good magnetic coupling and electrical characteristics.
2. Description of Related Art
Referring to FIGS. 1A and 1B, a traditional speaker 1 that is substantially rectangular includes a frame 10, a cover 11, a magnetic device 12, a voice coil 13, and a diaphragm 14. The magnetic device 12, the voice coil 13 and the diaphragm 14 are all disposed between the frame 10 and the cover 11. The magnetic device 12 includes a yoke 121, a magnet 122, and a pole piece 123. The magnet 122 and the pole piece 123 are sequentially mounted on the yoke 121. The voice coil 12 is integrated with the diaphragm 14. A repelling force or an attracting force is generated between the voice coil 13 and the magnet device 12 by the excitation of the magnetic device 12, which drives the diaphragm 14 to vibrate so as to generate a sound transmitted through the cover 11.
A conventional method for making the yoke 121 includes the following steps. A metal plate is first cut into a circular plate. The circular plate is then processed by stamping using a punching machine with a molding pillar. In this way, a protruding pillar 1211 is formed on a central portion of the circular plate. The protruding pillar 1211 enables other components (e.g., the magnet 122 and the pole piece 123) with central through holes to be mounted thereon.
However, the precision of forming the central pillar is generally not good when a noncircular metal plate is used in the stamping process. In addition, the evenness of the noncircular metal plate may not be good because of the different directions of the stresses. Hence, only circular plates are used to make the conventional yokes by stamping at present. Nevertheless, when a circular plate is used to make the yoke, it is required that the shapes of the through holes of the magnet, the pole piece, the voice coil and the frame are circular. When a circle is arranged on a given noncircular area, an area of the circle is limited by the fact that the width (i.e., a diameter of the circle) of the given noncircular area is less than the length of the given noncircular area. Accordingly, an area of a magnet arranged in a noncircular speaker (the speaker shown in FIGS. 1A and 1B is rectangular) can not be large enough. As a result, the electrical characteristic of the speaker is unsatisfactory. In addition, the height of the central protruding pillar is also limited because the yoke is made by stamping. Therefore, magnets with relatively great heights can not be employed in the speaker, which adversely affects the electrical characteristic of the speaker.
It is, therefore, desirable to provide a yoke, a method for making the yoke, and a speaker employing the yoke, with which the area of the magnet is increased so that the electrical characteristic of the speaker is improved.